Fingerprint recognition has become a standard configuration for smart phones. A fingerprint sensor is a key component for capturing a fingerprint. The fingerprint sensors may include optical fingerprint sensors, capacitance sensors, ultrasonic sensors and the like.
Sharpness of a fingerprint captured by the optical fingerprint sensor relates to luminance of light. The bigger the luminance is, the higher the sharpness is, and vice versa. At present, the light comes from a screen of the phone. However, the luminance of the screen is usually unchangeable.